HU220589B1 - Process for upgrading the flash zone gas oil stream from a delayed coker - Google Patents

Abstract

In the delayed coking process, the fractional column gas oil removed from the bottom of the fractionation column is improved by removing the suspended solid particles and then hydrogenated to make it more suitable for processing with a fluidized bed catalytic cracker or the like. Due to the removal of the solid particles, the material stream can be treated in a fixed bed catalytic hydrogenator without clogging the catalyst bed. ŕ

Description

The present invention relates to a process for improving gas oil discharged from a vaporizer zone of a delayed coke oven, and more particularly to a delayed coke oven, wherein vapors are introduced from the top of a coke chamber into a fractionation column, wherein said vapors are separated from a vapor stream.

A coking process of this type is described in U.S. Patent 4,518,487 (Graph et al.). According to the patent, product distribution is improved by removing gas oil from the bottom of the fractionation column and not returning it to the coking chamber as in previous coking processes.

Although the process described in U.S. Patent No. 4,518,487 provides significant improvements, it has the disadvantage that it is difficult to make gas oil from the steam zone suitable for further processing. The gas oil stream contains large amounts of finely divided solid particles and viscous mesophase material. The mesophase material is essentially liquid coke entrapped by vapors leaving the chamber. Said gas oil stream can be improved by hydrogenation. However, solids and mesophase material will rapidly break and contaminate the catalyst bed of the hydrogenator as power is passed through it. Non-hydrogenated gas oil can be processed in a fluid bed catalytic cracker (FCC) unit, but the product distribution of the non-hydrogenated stream is poor due to many aromatic components and other factors. Previous attempts to make the gas oil stream suitable for hydrotreatment by filtration have been unsuccessful, since the filter is rapidly clogged, difficulties in regenerating the filter medium, and so on.

According to the invention, substantially all solids that would otherwise contaminate the hydrogenation catalyst bed are removed by filtration from the gas oil stream from the evaporation zone. The stream containing the reduced amount of solids is then passed to a fixed bed catalytic hydrogenator, such as a hydrogen desulphurizer or hydrocracker, to reduce the sulfur content of the stream and to modify the molecular structure of the stream components for subsequent processing.

The product exiting a fluid bed catalytic cracker (FCC unit) has a significantly better distribution of hydrogenated gas oil than untreated gas oil.

The invention will now be described in more detail with reference to embodiments and drawings. In the drawings it is

Figure 1 is a schematic flow chart of a known coking process closest to the invention, a

Figure 2 is a schematic flow chart of the coking process of the present invention;

Figure 3 is a schematic diagram of a filter used in the process of the invention.

Figure 1 is a simplified flowchart of the coking process according to U.S. Patent No. 4,518,487. As shown in Figure 1, the starting material is fed through line 10 into the furnace 12 from where it enters a chamber 14 of the coke oven. From the top of the chamber 14, the vapors are introduced through a conduit into the fractionation column 18. A recirculated liquid, such as gas oil from coking, is sprayed through the conduit 20 into the vaporization zone of the fractionation column 18 to contact the incoming vapor to precipitate suspended particles and condense the higher boiling component of the incoming vapor stream. From the top of the fractionation column 18, the stream of wet gases is discharged through line 22 and intermediate liquid fractions through line 24 and 26. Gas oil containing suspended solids and viscous mesophase material is removed from the evaporation zone via a conduit 28 extending from the bottom of the fractionation column 18. In the prior art, the flash zone gas oil (FZGO) stream is typically added to a material fed to an FCC unit.

Figure 2 is a schematic diagram of the present invention. Components corresponding to Figure 1 are denoted by the same numerals. In Figure 2, gas oil from the evaporation zone is introduced into the filter 30. From the filter 30, gas oil is fed to a hydrogenation unit 32 and then to an FCC unit 34.

The hydrogenation unit 32 may be a desulphurisation unit or a hydrocracker by refining hydrogenation, but in each case a hydrogenation unit containing a fixed bed catalyst. In the prior art, the FZGO stream cannot be fed to a fixed bed catalytic hydrogenator because the suspended solids and viscous mesophase material rapidly contaminate the catalyst. As a result, the FZGO stream containing many aromatic components must be fed without filtration to an FCC unit, where product distribution is poor due to the high proportion of aromatic components. In addition, the FZGO stream often contains sulfur in amounts that are already causing problems with the product. In some cases, the FZGO stream may be used as a lower value stream, such as fuel in the process.

It was found that if substantially all of the suspended solids with a diameter greater than about 25 micrometers could be removed from the FZGO stream, the stream could be introduced into a fixed bed catalytic hydrogenator without damaging the catalyst bed. Particles larger than 25 micrometres make up most of the suspended solids, and the remaining small particles pass through the catalyst bed without causing significant contamination.

Any filter which effectively removes substantially all particles of 25 micrometers or larger can be used in the process of the invention. Filters that remove smaller particles up to 10 micrometers, for example, can be used, but are less and less economical.

An etched metal disk filter, available from PTI Technologies Inc. of Newbury Park, CA, is particularly effective. The etched

GB 220 589 B1 The metal disc filter consists of one or more filter elements, which are formed of several superposed discs and are particularly efficient, easy to regenerate, and relatively easy to operate and control. The regeneration step, which consists of purifying with high pressure gas, possibly followed by solvent rinsing, requires only half a minute to four minutes, so that the apparatus can be operated by a single filter unit, since the material to be introduced into the filter can be retained in an equalization tank or similar. Alternatively, two or more filter units are connected and regenerated separately, so that filtration is continuous.

Figure 3 is a schematic diagram of a preferred filtration system with the filter 30, the inlet line 36, the outlet line 38, the gas accumulator 40 and the collecting tank 42. During operation, FZGO enters filter 30 through line 36 and exits through filter 38. When the back pressure in the filter 30 reaches a preset level, the feed stops and opens a quick acting valve (not shown) on the gas accumulator 40. The pressurized gas flows back from the gas accumulator 40 through the filter unit 30 and washes or discharges the accumulated solid particles from the filter surface into the collecting container 42 or other suitable unit. Preferably, the filter is designed so that the cycle starts when the backpressure reaches a preset level. It has been found that the back pressure drops to near zero after the reflux purification cycle, indicating that the accumulated solids have been substantially completely removed. As mentioned earlier, after the pressure gas regeneration step, solvent rinsing can be performed if necessary.

The operation of the preferred embodiment of the present invention as shown in Figure 2 will now be described.

From the furnace 12, the material is introduced into one of the chambers 14 and the vapors are introduced into the bottom of the fractionation column 18. A heavy gas oil stream from line 20 is sprayed into the vaporization zone of fractionation column 18 where it contacts the feed material, condenses heavier components, and washes the suspended solids. From the evaporation zone, gas oil containing condensed vapors, solid particles and viscous mesophase material is discharged through line 28 from the fractionation column 18. The product streams leave the fractionation column 18 through the conduits 22, 24 and 26. From the evaporation zone, diesel oil (FGZO) passes through line 28 to filter 30, which removes suspended solids larger than about 25 micrometers. The filtered FZGO then flows to the catalytic hydrogenation unit 32 (preferably a desulphurisation unit) where the FZGO is desulfurized and / or modified for fluid bed catalytic cracking. The filtered FZGO does not contaminate the catalyst bed in the hydrogenator; Hydrogenated FZGO has a lower sulfur content and better distribution of the product leaving the FCC unit than non-sulfurized FZGO. As mentioned above, one or more filter units may be used with periodic or sequential rinsing to maintain permeability, and the removed solids may be used or deposited.

Example 1

In this example, 440 barrels of gas oil per stream were fed to a filter made of etched metal discs that removed particles larger than 25 micrometers. The filtered current was applied directly to an FCC unit during the first two weeks of the test period to verify that the filter had actually removed substantially all particles larger than 25 micrometers. After determining the efficiency of the filter, the filtered stream was fed to a fixed bed catalytic hydrogenator for several weeks.

The filter is designed to be automatically cleaning when the pressure drop is about 1.4 10 ⁵ Pa is reached in the filter. The pressure drop on the filter immediately after cleaning was close to zero, indicating the cleaning efficiency. During the filling cycle of the coke oven chamber, the filter was cleaned approximately every two hours.

In the gas oil from the evaporation zone, about 50% by volume of the particles was greater than 25 micrometers. The filtered stream contained no particles larger than 25 micrometers, and the proportion of particles in the filtered stream was low enough to cause no operational difficulties during the weeks when the filtered stream was fed to the hydrogenator. Table 1 shows the results of the filtration operation on the days when the suspended solids were analyzed.

Table 1

Group / Current FZGO (off) FZGO (off) FZGO (off) FZGO (off) FZGO (off) FZGO (off) test Day THE B C THE B C Total suspended solids by weight .0507 .0884 0,033 .0208 .0082 .0273 Distribution (micrometer) Volume% 1-2 2 0.05 0.12 0.05 0.13 0.03 0.12 2-4 4 1.90 7.52 3.41 5.97 2.03 6.64

HU 220 589 Bl

Table 1 (continued)

Group / Current FZGO (off) FZGO (off) FZGO (off) FZGO (off) FZGO (off) FZGO (off) test Day THE B C THE B C Total suspended solids by weight .0507 .0884 0,033 .0208 .0082 .0273 Distribution (micrometer) Volume% 4-8 8 4.63 22.22 14.25 29.19 8.70 23.31 8-16 16 7.11 25.90 18.29 36.08 35.65 32.99 16-22 22 9.95 14.74 12.61 28.63 53.58 36.94 22+ 76.36 29.50 51.39 0.00 0.00 0.00 Altogether 100.00 100.00 100.00 100.00 100.00 100.00

The above example illustrates the efficiency of an etched metal disk filter to remove suspended solids from gas oil so that the filtered stream can be processed in a fixed bed catalytic hydrogenator without contaminating the catalyst bed as in the case of non-harvested stream.

The invention has been described and illustrated by the above exemplary embodiments; of course, many further changes and modifications can be made without departing from the spirit or scope of the invention.

Claims (8)

PATENT CLAIMS A process for delayed coking, wherein vapors are introduced from the top of a coke chamber into a fractionation column, wherein said vapors are characterized by a gas stream containing a significant amount of solid particles, separated from the vapor stream, intermediate liquid streams and the vaporization zone, a) reducing the amount of solid particles in the gas oil discharged from the evaporation zone by filtration; and b) after step a), the filtered gas oil stream is fed to a fixed bed catalytic hydrogenation unit. 45 A process according to claim 1, characterized in that said filtration step comprises substantially all Solid particles larger than 25 micrometers are removed. The process according to claim 1, wherein said catalytic hydrogenation unit is a hydrocracking unit. The process according to claim 1, wherein said catalytic hydrogenation unit is a hydrogen sulfonator. 5. A process according to claim 4, wherein the desulphurized gas oil from the hydrotreater is fed to a fluid bed catalytic cracker (FCC) unit. The process of claim 1, wherein said filtration step comprises etching metal 35 using a filter element made up of discs. 7. The method of claim 6, wherein said filter element is periodically refluxed. The method of claim 7, wherein said plurality of filter elements are used which are sequentially cleaned, each time maintaining at least one filter element to remove solid particles in gas oil.